Impact of Surface Composition Changes on the CO₂-Reduction Performance of Au-Cu Aerogels

Over the past decades, the electrochemical CO₂-reduction reaction (CO₂RR) has emerged as a promising option for facilitating intermittent energy storage while generating industrial raw materials of economic relevance such as CO. Recent studies have reported that Au-Cu bimetallic nanocatalysts feature a superior CO₂-to-CO conversion as compared with the monometallic components, thus improving the noble metal utilization. Under this premise and with the added advantage of a suppressed H₂-evolution reaction due to absence of a carbon support, herein, we employ bimetallic Au₃Cu and AuCu aerogels (with a web thickness ≈7 nm) as CO₂-reduction electrocatalysts in 0.5 M KHCO₃ and compare their performance with that of a monometallic Au aerogel. We supplement this by investigating how the CO₂RR-performance of these materials is affected by their surface composition, which we modified by systematically dissolving a part of their Cu-content using cyclic voltammetry (CV). To this end, the effect of this CV-driven composition change on the electrochemical surface area is quantified via Pb underpotential deposition, and the local structural and compositional changes are visually assessed by employing identical-location transmission electron microscopy and energy-dispersive X-ray analyses. When compared to the pristine aerogels, the CV-treated samples displayed superior CO Faradaic efficiencies (≈68 vs ≈92% for Au₃Cu and ≈34 vs ≈87% for AuCu) and CO partial currents, with the AuCu aerogel outperforming the Au₃Cu and Au counterparts in terms of Au-mass normalized CO currents among the CV-treated samples.